Shear bands and cracking of metallic glass plates in bending light

The thickness dependence of yielding and fracture of metallic glass plates subjected to bending is considered in terms of the shear band processes responsible for these properties. Crazing frequently precedes fracture in some glassy thermoplastic polymers. In this study, the deformation mechanisms of bulk metallic glass bmg foam with around 49% porosity were investigated by using xray computed tomography ct technique. Development of tough, lowdensity titaniumbased bulk. A theoretical model, which predicts such a shear band zone at the crack tip, is used to discuss the elasticplastic response of the metallic glass. Based on the moritanakas mean field concept, a micromechanicsbased incremental damage theory was developed to investigate the mechanical performance of bulk metallic glass matrix composites unde. Schuh department of materials science and engineering, massachusetts institute of technology, cambridge, ma 029, usa. E ective temperature dynamics of shear bands in metallic glasses eric g.

Upon yielding, shear strain in mgs is highly localized into narrow, 10nmwide bands. Laser remelting has previously been found to be an excellent method of fabricating thick 250 5m surface layers, and the glass forming composition chosen. While shear bands are ubiquitous in many types of materials section 1. Direct observations on the evolution of shear bands into cracks in metallic glass ruitao qu shenyang national laboratory for materials science, institute of metal research, chinese academy of sciences, shenyang 110016, peoples republic of china fufa wu. Details of the experimental measurement are described in methods. Bulk metallic glasses bmgs can exhibit excellent combinations of strength. Bending of plates, or plate bending, refers to the deflection of a plate perpendicular to the plane of the plate under the action of external forces and moments. Astm d6272 flexural properties testing of unreinforced. The corollary from this finding is that shear bands can interact with. It suggests that the deformation of metallic glasses is sensitive to local stress. Shear bands and cracking of metallic glass plates in bending core. Scratch test induced shear banding in high power laser.

In order to examine whether there are some internal cracks inside the msb, sem and xrt imaging were performed on a sample compressed to the critical state at which catastrophic instant fracture was about to occur, as shown in fig. Experimental observations of shear band nucleation and propagation in a bulk metallic glass. Temperature rise at shear bands in metallic glasses. Similar to those in many other materials, shear bands in metallic glasses are only active for a very short time, which directed research focus towards topological, structural, chemical, and thermal properties of formed. Initiation of shear bands near a stress concentration in. Meanwhile, by using the fusible coating method, thermal effect on shear bands was investigated. Feb 08, 2011 semisolid processing of bulk metallic glass matrix composites. Shear bands topology in the deformed bulk metallic glasses mdpi.

Temperature rise at shear bands in metallic glasses j. Making metallic glasses plastic by control of residual. Making metallic glasses plastic by control of residual stress. Astm d6272 flexural properties testing of unreinforced and reinforced plastics by fourpoint bending. Long range stress fields and cavitation along a shear band. Shear band spacing under bending of zrbased metallic. For two different sbs in one specimen, the critical shear offsets maintain approximately the same value, which sheds light on the critical shear failure condition of metallic glass. The ingots with diameters from 1 up to 4 mm were successfully obtained. Feb 22, 2016 fracture experiment of a pdcusi metallic glass. The minimum shear offsets necessary to detect local heating are determined. Department of materials science and engineering, case western reserve university, 10900 euclid avenue, cleveland, ohio 44106, usa. The thickness dependence of yielding and fracture of metallic glass plates subjected to bending is considered in terms of the shear band. Research in our group has covered a wide range of topics in metallic glasses, ranging from alloy design including the development of novel metallic glass matrix composite materials and studies of the atomicscale structure to very practical studies of mechanical behavior, including both deformation and fracture. Plastic deformation of metallic glasses mgs has long been considered to be.

Designing metallic glass matrix composites with high. This work shows that shear band spacing in metallic glass plates in bending varies linearly with plate thickness, at a ratio of. Designed heterogeneities improve the fracture reliability. Origin of ultrafast ag radiotracer diffusion in shear bands of deformed bulk metallic glass pd40ni40p20. Deformation and fracture behavior of tungsten fiber. Stickslip dynamics and recent insights into shear banding. Volkert1 1institute for materials physics, university of gottingen, friedrichhund platz 1, 37077 g ottingen, germany. Shear band spacing under bending of zrbased metallic glass. Similar to those in many other materials, shear bands in metallic glasses are only active for a very short time, which directed research focus towards topological, structural, chemical, and thermal properties of formed, but inactive shear bands. The main conclusions will shed some light on optimizing the.

Xray ct experiments were conducted at esrf synchrotron source, grenoble, france where the insitu compression testing is possible. Metallic glasses materials science and engineering. Localized crystallization in shear bands of a metallic glass. Greer department of materials science and metallurgy, university of cambridge, pembroke street, cambridge cb2 3qz, uk permanent address. Shear bands introduced into the asquenched metallic glass alloy, metglas r 2826 fe 40 ni 40 p 14 b 6, were etched by immersion in a solution of cus04 and hci elimination of the etchability property through isothermal annealing had an apparent activation enthalpy of 250 kj mol. Using scanning electron microscopythey showed that both. Shear bands and cracking of metallic glass plates in bending r. Shear bands introduced into the asquenched metallic glass alloy, metglas r 2826 fe 40 ni 40 p 14 b 6, were etched by immersion in a solution of cus04 and hci. Therefore, because the shear bands are more widely spaced in thicker plates, and the shear offsets are larger, crack initiation in the shear bands is expected to occur more readily in thicker plates. The typical deformation and fracture features of ductile metallic glasses are the formation of shear bands and shear fracture with a well developed vein pattern on the fracture surface wright et al. Amazing biggest steel bending machine at work, fast. Noting the similarity between an operating shear band and a mode ii or mixed mode crack. Despite high strength and elasticity combined with plasticlike processing ability, wide spread proliferation of metallic glasses mgs in structural applications has been stymied by their lack of tensile ductility. By experimenting first with the size of the dendrites, hofmann and his colleagues noted that when metallic glasses were bent, 10nanometerwide features called shear bands rip right through glass that is thicker than one millimeter, but are stabilized in thin glass.

D shear bands and cracking of metallic glass plates in bending. Nanomechanical properties along a single shear band in a zrbased metallic glass were studied. Initiation of shear bands near a stress concentration in metallic glass c. Both shear band offset and shear band spacing increase with increasing curvature, as the square of the plate thickness. Elimination of the etchability property through isothermal annealing had an apparent activation enthalpy of 250 kj mol. Here by threepoint bending test on a typical ductile pdcusi metallic glass, we. Shear band feature in two bulk metallic glasses with. Based on the moritanakas mean field concept, a micromechanicsbased incremental damage theory was developed to investigate the mechanical performance of bulk metallic glass matrix composites under tension. Ti dendrites reinforced cu 47 ti 34 zr 11 ni 8 bulk metallic glass bmg composite ingots were prepared by the suction casting method. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction. There is no need to be concerned about degraded properties through disruptions. Adiabatic shear band formation in metallic glasses intechopen.

Shear band formation and cracking of a metallic glass. Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Designing metallic glass matrix composites with high toughness and tensile ductility. Theory of shear banding in metallic glasses and molecular. Thus the bend ductility is pre dicted to decrease with increasing plate thickness because the shear band spacings and shear offsets are larger in. Annealing of shear bands in metallic glasses springerlink. We created shear bands by bending the ribbons to 180 refs. Shear band relaxation in a deformed bulk metallic glass. The significant difference in plastic deformation ability can be ascribed to different shear banding features. Shear bands and cracking of metallic glass plates in. Continued bending leads to crack formation and failure. Amazing biggest steel bending machine at work, fast extreme large plate rolling machines. The macroscopic tensile plasticity of bulk metallic glasses bmgs is highly desirable for various engineering applications. Semisolid processing of bulk metallic glass matrix.

Shear bands and cracking of metallic glass plates in bending, journal of applied physics, jul. Sizedependent fracture toughness of bulk metallic glasses. The model predicts the existence of a critical lengthscale. Indeed, extensive shear band formation and crack tip blunting in front of a. Local temperature rises during mechanical testing of metallic.

Schuh department of materials science and engineering, massachusetts. We limit our discussions to the materialsscience aspects of shear bands. Development of tough, lowdensity titaniumbased bulk metallic glass matrix composites with tensile ductility. Designing tensile ductility in metallic glasses nature. Jun 01, 2008 read evolution of shear bands in bulk metallic glasses under dynamic loading, journal of the mechanics and physics of solids on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Johnson materials science group, keck laboratory, california institute of technology, pasadena, california 91125. The collected ct images were digitally enhanced and the volumetric strain of the foam cells. Metallic glasses or amorphous metals are novel engineering alloys in which the structure is not crystalline as it is in most metals but rather is disordered, with the atoms occupying moreorless random positions in the structure. We argue that the shear band spacing and length scales with the thickness of the plate because of strain relaxation in the vicinity of the shear band at the surface.

Spatial mapping of both indentation hardness and modulu. May 03, 2004 a crack forms when the strain can no longer be accommodated by the generation of many shear bands. Direct microscopic observations indicated that the etching of. As bending is increased beyond yield, shear band spacing continues to increase until the strain is accommodated by a few long shear bands.

Bending was performed using two parallel plates fixed at the two sides of a vernier caliper. E ective temperature dynamics of shear bands in metallic glasses. Such extreme localization of plastic deformation, within a thicker liquidlike layer implied by fracturesurface morphology, cannot have a thermal origin. In this sense, metallic glasses are similar to the more familiar oxide glasses such as the sodalime glasses used for windows and bottles.

Critical fictive temperature for plasticity in metallic. The shear band controlled deformation in metallic glass. Experimental observations of shear band nucleation and. Here by threepoint bending test on a typical ductile pdcusi.

While thick plates of bmg are well known to fail catastrophically in. Jun 26, 2003 the thickness dependence of yielding and fracture of metallic glass plates subjected to bending is considered in terms of the shear band processes responsible for these properties. Adapting calculations for the heating at a crack tip, the shearing generates a line source of heat6,andthepredicted rise is a few tens of kelvin. Under ambient conditions, plastic flow in metallic glasses is sharply localized into shear bands.

Paton, ne 2003 shear bands and cracking of metallic glass plates in bending. The shear offsets associated with each shear band must also scale with the length of the shear band, thus increasing with plate thickness. The rational design of tough metallic glasses, however, remains challenging because of the inability of existing theories to capture the correlation between plasticity, composition and processing for a wide range of glass forming alloys. The agedrejuvenationglueliquid argl shear band model has been proposed for metallic glasses acta mater. Chapter 3 correlation between fracture surface morphology. The heat content of, and consequent temperature rise at, shear bands in three bulk metallic glasses are compared using a recently reported fusible coating method. However, the shear band morphology in mode i cracktip stress field is. Apr 25, 2016 relaxation of shear bands in a pd 40 ni 40 p 20 bulk metallic glass was investigated by radiotracer diffusion allowing to determine for the first time the effective activation enthalpy of diffusion along shear bands in a deformed glass. They are used in micromirrors used in digital light processor dlp.

As a metallic glass is subjected to deformation at the temperature far below its glass transition temperature at the level of the shear yield stress, inhomogeneous plastic deformation occurs with the characteristic of formation of localized shear bands fig. Feb 22, 2016 the shear band controlled deformation in metallic glass. The socalled shear bands are typical indicators of irreversible damage and eventually cause fracture. The motion of atoms in a shear band locally transforms the glass to a lower. Shear bands were introduced into a zrticunial bulk metallic glass bmg by onedirectional cold rolling and the effect on fracture toughness aniso.

Small stress relieving cracks nucleate within the polymer parallel to the direction of maximum shear stress at an angle of 45. The work sheds lights on the underlying physics of the failure criterion. Local temperature rises during mechanical testing of. The shear bands are in parallel to the bending axis, and the spacing between adjacent shear bands ranges fig. Shearband affected zone revealed by magnetic domains in a. A crack forms when the strain can no longer be accommodated by the generation of many shear bands. Discovery of anomalous softening phenomenon and shear bands. Stereophotogrammetric investigation of overload and cyclic fatigue fracture surface morphologies in a zrtini cube bulk metallic glass.

As the number of shear bands accumulates the overall strain of the material increases. A longsought goal in metallic glasses is to impart ductility without conceding their strength and elastic limit. It was shown that introducing tic microsized particles into the amorphous matrix did not disturb the glass forming ability gfa of the matrix. Request pdf analysis of shear banding in metallic glasses under bending an. A micromechanicsbased incremental damage theory of bulk.

The bending experiments told us that the size of the particles we need to. Shear bands and cracking of metallic glass plates in bending. Correlation between fracture surface morphology and. Role of preexisting shear band morphology in controlling. Nov 15, 2012 a research team from japan has discovered an anomalous softening effect in metallic glass, in which the hardness and elastic modulus of the material are reduced remarkably by applying giant shear.

The precursor 11,12 of shear bands in metallic glasses is the appearance of some regions that undergo local yielding, the socalled shear transformation zones stzs 1415, which consist. Bulk metallic glasses bmgs and their derivative metal matrix composites bmgmcs are emerging highperformance engineering materials that are on the precipice of widespread commercialization. Direct observations on the evolution of shear bands into. Analysis of shear banding in metallic glasses under bending. We argue that the effect of plate thickness on the deformation and fracture properties of metallic glasses in bending can be understood in terms of the shear bands that develop during plastic. To reveal the difference of such shear band controlled deformation from the conventional materials mechanics, we performed 3point bending test on a notched pd 77. Following from this, the next step in our analysis is a. Shear banding is produced in polymers when they are exposed to compressive stresses. In this chapter, shear band formation process in metallic glasses is. Shear band spacing under bending of zrbased metallic glass plates. It should be noted that no cracks are observed in all afm images. To reveal the difference of such shear band controlled deformation from the conventional materials mechanics, we performed 3point bending test on. For the first time, a direct experimental mapping of crack tip plasticity, in the form of an elliptical shear band zone, has been recorded.